For waveguides of outdoor type, when moist air or water penetrates in a waveguide from the connecting face of a flange, there is a possibility of the waveguide to corrode.
For this reason, airtight and/or watertight structure with a gasket and the like is used in every connecting face of a flange, in order to prevent the humidity or moisture to penetrate in a waveguide.
When waveguides of outdoor type are being placed, it is ideal to unify the materials of the waveguides, however in reality, waveguides formed in heterogeneous metals may have to be connected to each other.
When connecting together the heterogeneous metal waveguides, because the heterogeneous metals are connected to each other in a section outer side of a gasket of a connecting face of a flange, if humidity or moisture is supplied thereto, an electrolytic corrosion occurs due to a formation of a local cell, and an anode metal will corrode.
The greater the redox potential difference between the heterogeneous metal is (in other words, the greater the difference of the ionization tendency is), the quicker an electrolytic corrosion progresses, therefore when connecting waveguides of heterogeneous metals, a method of by inserting a metal having the intermediate electric potential of the metal thereof and having the redox potential difference low in a flange section of each waveguide is being used.
For example, when connecting aluminum alloy waveguide and copper alloy waveguide, the structure of inserting stainless alloy flange, which has the intermediate electric potential, between each flange section is used in order to prevent an electrolytic corrosion due to the potential difference.
However, the material itself of a stainless alloy is expensive compared to aluminum alloy and copper alloy and the like, as well as the processing cost because the processing is difficult. For this reason, the production cost of metal parts made from stainless alloy becomes high. In particular, when a gasket is attached on both sides of a flange, in addition to make the flange section thick according to the depth of the groove necessary for the attachment of a gasket, the production cost becomes high in order to process a groove on both sides of a flange.
Furthermore, the number of the connection face of a waveguide flange will increase, and as shown in FIG. 1 or FIG. 2, there will be more parts to be airtight and/or watertight by using a gasket and the like.
The art related to the structure of connecting a tubular member as suppressing the occurrence of an electrolytic corrosion is disclosed in patent document 1 as “insulation flange”. The patent document 1 is for ensuring the airtightness and/or watertightness of a pipe as preventing an electrolytic corrosion, by having an insulator impressed with an annular groove between a pair of flange placed, and by having a packing for sealing on the annular groove.
Patent document 1: Laid-Open Japanese Utility Model Publication No. Sho 61-112191